生物化學(xué)資料：chapter 9 Tricarboxylic Acid Cycle

1、Biochemistry,Chapter 9 Tricarboxylic Acid Cycle,The decarboxylation of pyruvate, and the oxidation of acetate takes place in the mitochondrial matrix,ATP synthesis takes place in the inner membrane,Glucose Pyruvate Acetal-CoA TCA Cycle,NAD,NADH +H,CoA-SH,CO2,CO2 + H2O,Glycolysis,Yielding of acetyl-C

2、oA,acetyl-CoA is oxidized,TCA,The Nobel Prize in Physiology or Medicine 1953,for his discovery of the citric acid cycle,尿素循環(huán),Pyruvate is transported into mitochondria（線粒體） then oxidized to acetyl-CoA (releasing CO2) before entering the citric acid cycle,Pyruvate is oxidized to acetyl-CoA,丙酮酸脫氫酶系,thr

3、ee enzymes,six coenzymes,PDH complex,pyruvate dehydrogenase (E1,dihydrolipoyl transacetylase (E2,dihydrolipoyl dehydrogenase (E3,CoA-SH NAD+/NADHH+ Lipoate (硫辛酸） FAD TPP Mg2,Regular proteins,Protein kinase Phosphate protein phosphatase,Pyruvate dehydrogenase complex,二氫硫辛酰轉(zhuǎn)乙?；?二氫硫辛酸脫氫酶,硫胺素焦磷酸Vb1,腳氣病

4、,The process of oxidation from Pyruvate to acetyl-CoA,丙酮酸與TPP結(jié)合并脫羧形成羥乙基TPP。 2. 羥乙基TPP氧化轉(zhuǎn)變成乙?；瑫r(shí)轉(zhuǎn)移到E2的輔基硫辛酰胺上。 3. 在E2上的乙?；贓2催化下轉(zhuǎn)移到CoASH 上形成游離的乙酰CoA.從而形成了一個(gè)高能硫酯鍵,4. 還原型的E2將二個(gè)SH基H轉(zhuǎn)移到E3的輔酶FAD上形成還原型FADH,5. E3上的還原型的FADH將H交給NAD+形成NADH，E3輔基又形成氧化型的FAD,20,5-6,60,Pyruvate dehydrogenase complex,二氫硫辛酰轉(zhuǎn)乙?；?二氫硫辛

5、酸脫氫酶,硫辛酸,共價(jià) 相連,Electron Micrograph of pyruvate dehydrogenase complexes,受蛋白激酶和磷酸蛋白磷酸酶控制磷酸化失活 E1的磷酸化和去磷酸化是使PDH復(fù)合體失活和激活的重要方式. 受激素調(diào)節(jié) 受能荷效應(yīng)物調(diào)節(jié) （變構(gòu)調(diào)節(jié),激活劑,ADP, AMP,E1,CoASH, NAD,E2, E3,抑制劑,ATP, GTP,E1,Acetal-CoA NADHH,E2, E3,Regulation of pyruvate dehydrogenase complex,Regulation of pyruvate dehydrogenase

6、complex,砷化物可與丙酮酸脫氫酶復(fù)合物中E2輔基硫辛酰胺的巰基發(fā)生共價(jià)結(jié)合，使還原型硫辛酰胺形成失去催化能力的砷化物,拿破侖之死,砒霜是如何使拿破侖中毒并死亡的呢？Do you know,生活中砒霜的形成,法國(guó)人：繼承粉末,蝦體內(nèi)所含砷的化學(xué)價(jià)是五價(jià)，一般情況下，五價(jià)砷對(duì)人體是沒有害處的。理論上講，高劑量的維生素C（一次性攝入維生素C超過(guò)500毫克）和五價(jià)砷經(jīng)過(guò)復(fù)雜的化學(xué)反應(yīng)，會(huì)轉(zhuǎn)變?yōu)橛卸镜娜齼r(jià)砷（即我們常說(shuō)的“砒霜”），當(dāng)三價(jià)砷達(dá)到一定劑量時(shí)可導(dǎo)致人體中毒,維生素C和蝦,乙酰CoA,檸檬酸,順烏頭酸,異檸檬酸,a-酮戊二酸,琥珀酰CoA,琥珀酸,蘋果酸,延胡索酸,草酰乙酸,Tricar

7、boxylic Acid Cycle,Each acetyl-CoA is completely oxidized to two CO2, generating three NADH, one FADH2, and one GTP; The metabolites contain six, five or four carbons in the cycle,NAD+ and FAD takes the electrons during acetyl-CoA oxidation,The cycle begins with the condensation of acetyle-CoA and o

8、xaloacetate to form citrate,草酰乙酸,檸檬酸,檸檬酸合酶,The hydrolysis of the high energy thioester(硫酯) drives the reaction,催化TCA的第一步反應(yīng)，反應(yīng)先生成檸檬酰CoA，再水解為檸檬酸，是放能反應(yīng)，不可逆；是TCA的第一個(gè)調(diào)節(jié)酶，活性受ATP、NADH、Succinyl CoA(琥珀酰CoA)及長(zhǎng)鏈脂酰CoA的抑制，對(duì)于TCA是一個(gè)rate-limiting step。 氟乙酰CoA在酶的作用下可與草酰乙酸生成氟檸檬酸，順烏頭酸酶只識(shí)別檸檬酸，對(duì)氟檸檬酸沒有作用，致使TCA中斷，這種合成為致死合

9、成(lethal synthesis)。在代謝研究的應(yīng)用上，曾被廣泛用于殺蟲劑或滅鼠藥的生產(chǎn) (現(xiàn)已被明令禁止),Citric acid synthase,G0 = 8.4 kJ/mol,G0 = -2.1 kJ/mol,90,4,6,Fluoride citrate（氟檸檬酸） is the special inhbitor of aconitase,Citrate isomerizes to isocitrate (異檸檬酸) via cis-aconitate (順烏頭酸,Aconitase (烏頭酸酶,反應(yīng)具有嚴(yán)格的空間特異性,Reaction 4 and 5,Isocitrate u

10、ndergoes oxidative decarboxylation (氧化脫羧) to form a-ketoglutarate (a-酮戊二酸,Isocitrate is oxidized (第一次脫氫) and decarboxylated.(第一次脫羧) 既有以NAD+為輔酶的異檸檬酸脫氫酶，也有以NADP+為輔酶的異檸檬酸脫氫酶 Positive effectors: ADP, AMP, isocitrate Negative effectors: ATP, NADH,異檸檬酸脫氫酶,Catalyzed by -ketoglutarate dehydrogenase complex;

11、 almost the same as pyruvate dehydrogenase complex; E3 is identical (相同的), E1 and E2 are very similar. 第二次脫氫,第二次脫羧.E1酶不受磷酸共價(jià)調(diào)節(jié). Reaction requires TPP and lipoate etc(6種輔酶,ketoglutarate undergoes oxidative decarboyxlation to form succinyl-CoA (琥珀酰CoA,a-酮戊二酸脫氫酶系,琥珀酰CoA合成酶 （也稱琥珀酸硫激酶,Cleavage of the thi

12、oester bond (硫酯鍵) in succinyl-CoA is coupled to GTP (or ATP) formation,The third example of substrate-level phosphorylation,琥珀酰CoA,琥珀酸,琥珀酸是對(duì)稱分子,沒有了手性,Cleavage of the thioester bond (硫酯鍵) in succinyl-CoA is coupled to GTP (or ATP) formation,琥珀酰CoA合成酶,琥珀酸,延胡索酸,Succinate is oxidized to fumarate (延胡索酸,琥

13、珀酸脫氫酶,The free energy change of this reaction is insufficient to reduce NAD+. Succinate Dehydrogenase is directly linked with the electron transport chain,三羧酸循環(huán)中唯一與內(nèi)膜結(jié)合的酶，是脫氫酶中最重要的酶,TCA循環(huán)階段,琥珀酸脫氫酶的鐵硫聚簇,FAD和琥珀酸脫氫酶的共價(jià)結(jié)合,丙二酸 琥珀酸（丁二酸,Succinate is oxidized to fumarate (延胡索酸,1. The enzyme catalyzes stereo

14、specific dehydrogenation 2. Malonate (丙二酸) is the inhibitor of the reaction,該酶具有嚴(yán)格的立體專一性，即只生成反式延胡索酸； 與琥珀酸結(jié)構(gòu)類似的化合物如丙二酸、戌二酸等是該酶的競(jìng)爭(zhēng)性抑制劑,延胡索酸,蘋果酸,Fumarate is hydrated to L-malate (蘋果酸,延胡索酸酶,Hydration(水合,該酶具有嚴(yán)格的立體專一性，即只生成L-蘋果酸,or,Oxaloacetate (草酰乙酸) is regenerated by the oxidation of L-malate (蘋果酸,The st

15、andard free energy of this reaction is very positive. The oxidation of malate is driven by the efficient removal of the products,蘋果酸脫氫酶,TCA循環(huán)階段,蘋果酸脫氫酶的結(jié)構(gòu),The last three reactions of the of the TCA cycle are similar to fatty acid degradation and synthesis, and some amino acid degradations. oxidation

16、hydration oxidation,A methylene group (CH2) is converted to a carbonyl group (C=O,The last three reactions of the of the TCA cycle,1. 總反應(yīng)式: CH3-C-SCoA + 3NAD+ + FAD + GDP + Pi 2CO2 + 3NADHH+ + 1FADH2 + 1GTP + CoA-SH,2. There are two carbon atoms in the form of acetyl-SCoA enters every cycle; and the

17、re are two decarboxylations take place in each cycle; 乙酰輔酶A中的二碳乙?；M(jìn)入TCA循環(huán)；在循環(huán)中發(fā)生兩次脫羧反應(yīng). Notice: the 2 carbon atoms entering the cycle are not the same as those leaving the cycle,Survey of TCA cycle,3. There are four dehydrogenation reactions take place in each cycle; 在循環(huán)中發(fā)生四次脫氫反應(yīng)(3NADH,1FADH2,4. The

18、re is a substrate level phosphoralation; 循環(huán)中發(fā)生一次底物水平磷酸化,Survey of TCA cycle,5. The reactions catalyzed by aconitase and fumarase is asymmetry reactions; 順烏頭酸酶和延胡索酸酶等催化非對(duì)稱反應(yīng) 6. All of the intermediary metabolisms are not synthesis and decomposition net. 所有中間代謝產(chǎn)物在代謝中沒有凈合成或凈降解,Survey of TCA cycle,Acety

19、l in acetyl-S-CoA was oxydized: 化學(xué)氧化釋放的自由能：874.9 kJ/mol 生物氧化釋放的自由能：520.9 kJ/mol 用于ATP合成的自由能：354 kJ/mol,The energetic of the aerobic decomposition of glucose,2. Hydrations in TCA-cycle,The third H2O entered in TCA cycle,Citryl-CoA+H2O succinyl-CoA + H2O Fumarate+H2O,Citrate+ CoA-SH Succidate + CoA-SH

20、 Matalte,H2O,H2O,The energetic of the aerobic decomposition of glucose,H2O,3. Dehydrogenations in oxydation of glucose,The energetic of the aerobic decomposition of glucose,4. Caculation of energy,In EMP,ATP 4 - 2,Numbers of ATP,2NADHH+ 2 2.5,In formation of acetyl-CoA,2NADHH+ 2 2.5,In TCA cycle,3NA

21、DHH+ 2 3 2.5 2,FADH2 2 1 1.5 2,GTP 2 1 1 2,Summery: 32,FADH2,2 1.5,30,The energetic of the aerobic decomposition of glucose,The reaction of TCA cycle,1. All organic chemicals can be completely oxidized to CO2 and H2O via a cycled pathway; 所有的有機(jī)化合物都可以通過(guò)TCA環(huán)徹底降解為CO2 和 H2O ; 2. Plenty energy can be pro

22、vided accompany the cycled pathway; 伴隨著這一循環(huán)途徑，大量的自由能被轉(zhuǎn)換,Significance of TCA,3. The intermediates in the cycle are important sources for biosynthetic precursors; TCA環(huán)中的中間代謝產(chǎn)物是重要的生物合成的前體 4. The cycle is an amphibolic pathway, and is a metabolic hinge of all biochemicals TCA環(huán)是一個(gè)分解合成無(wú)定向途徑，是所有生物化合物的代謝樞紐。

23、分解產(chǎn)能,合成前體,Significance of TCA,In addition to generating reducing potential, the TCA cycle also provides molecules for biosynthetic pathways. Also, the TCA cycle is an entry point for degradative pathways such as amino acid catabolism. Thus, the TCA cycle is highly regulated,TCA Cycle Regulation (TCA

24、循環(huán)的調(diào)節(jié),Regulation of the PDH Complex,High concentrations of the reaction products of the PDH complex inhibit activity: NADH Acetyl CoA This makes sense because it indicates the cell is rich in energy,Regulation of the PDH Complex,The PDH complex is covalently modified by phosphorylation. Phosphorylation inactivates the complex. Dephosphorylation activates the complex,When the energy charge is high the PDH kinase is